1. Field of the Invention
The disclosed mechanism and method relates to an image forming apparatus, and more particularly to an image forming apparatus that includes a rotary image-developing station which is capable of efficiently supplying developers to multiple image-developing units without a time delay.
2. Discussion of the Background
An image forming apparatus that adopts a rotary image developing station using a plurality of color developers (e.g., toner) has been placed on the market. The rotary image-developing station generally includes a plurality of image-developing devices each for developing an image using a developer and a supporting member for supporting the image-developing devices. The supporting member is disposed in front of an image bearing member that bears a latent (to-be-developed) image thereon, and has a rotary axis in parallel to the rotary axis of the image bearing member.
Accordingly, a rotation of the supporting member causes the image-developing devices to revolve around the rotary axis of the supporting member. Each of the image-developing devices includes a developer container that contains a developer to be used for developing the latent image formed on the image bearing member. The revolving movement of the image-developing devices may be controlled to bring each of the image-developing devices individually to a position where an image-developing operation may be performed relative to the latent image formed on the image bearing member.
Many of the above-described rotary image-developing stations employ a developer container that typically has an opening for passing a developer and that rotates together with the image-developing device so that the developer drops around the opening by its own weight inside the developer container. Then, the developer passes to the image-developing device.
In the thus configured rotary image-developing station, a control of supplying developer is crucially important to prevent the image-developing device from containing an excessively large or small amount of developer. This is the case because the supplying amount of the developer to the image developing device from the developer container relies on the rotational movement of the developer container but not on the amount of developer remaining in the image-developing device.
If the image-developing device contains an excessively large or small amount of developer, an image may be developed in an improper image density on the image bearing member.
Therefore, many of the rotary image-developing stations employ a developer supply amount controller at an inside of a casing of the image-developing device to control the supply amount of developer. The developer supply amount controller has a developer inlet which fits to the opening of the developer container to receive a developer from the opening of the developer container. The developer supply amount controller controls the supply amount of the developer to the image-developing device.
Keeping in line with the recent downsizing trend of image forming apparatus, the developer supply amount controller as well as the rotary image-developing station are required to be smaller. Consequently, the opening of the image-developing device and the inlet of the developer supply amount controller are required to be compact in size as well. As a result, the developer container cannot be made in an arbitrary shape but is in a special flat shape in order to discharge all the developer in the developer container, using a drop by its own weight, through the small opening to outside of the developer container.
However, there is a case in which the developer container cannot be made in the above-mentioned preferred special flat shape. For example, the applicants of the present invention have proposed an image forming apparatus which has a retractable rotary image-developing station in Japanese Patent Application No. 9-208705 (1997), improving the maintainability of the individual image-developing device.
In this retractable rotary image-developing station, a toner bottle is used as a developer container and is configured in a cylindrical shape rather than the special flat shape so as to be efficiently accommodated by the supporting member. Also, in this retractable rotary image-developing station, the toner bottle is provided with a developer conveying member (hereinafter referred to as an agitator) which transfers toner inside the toner bottle to completely discharge the toner in the toner bottle through the opening thereof. However, since the toner bottle is consumable and is disposed of when finished, the agitator provided therein is also disposed of together with the developer container. Accordingly, the developer container having an expensive agitator therein results in not only increasing a running cost per copy, but also causing problems in aspects of natural resource conservation and global environmental protection.
Based on the above result, the applicants of the present invention have proposed an improved developer container (e.g. toner bottle) in Japanese Patent Laid-open application No. 9-287976 (1997). Such a developer container is in a cylindrical shape, revolving around the rotation axis of the rotary image-developing station, and is capable of supplying the developer without using the agitator. This developer container includes a special guide formed on an inner wall of the developer container so that the developer is conveyed to the opening along the guide inside the developer container as the rotary image-developing station rotates.
The above-mentioned improved developer container is also capable of conveying the developer in different directions by mounting more than one block of the guide. Furthermore, the guide of the inner wall is made in a form of a spiral projection, so that the manufacturing cost of the developer container is further reduced and, as a result, the running cost per copy is also reduced.
However, the above-mentioned improved developer container has a problem. The problem is that the developer in the improved developer container can be transferred to the image-developing device only when the developer container revolves by the rotation movement of the rotary image-developing station.
Accordingly, when an event that one of the image-developing devices has an excessively decreased amount of developer is detected, the rotary image-developing station is required to rotate so that the developer container moves and the developer in the developer container is transferred to the image-developing device. At this time, the developer in the developer container is conveyed to the inlet of the image-developing device through the opening of the developer container by the rotating movement of the rotary image-developing station, which movement is controlled to continue for a predetermined time period.
That is, in this image forming apparatus, the rotary image-developing station is required to rotate for a certain time period in order to move the developer container to supply the developer into the image-developing device when the image-developing device in operation has a smaller amount of developer relative to a predetermined value. This rotating movement of the rotary image-developing station to supply the developer into the image-developing device interrupts the copying operation. Accordingly, the operator needs to wait until filling of the developer is completed before the copying operation is executed.
As described above, the developer supplying operation from the developer container to the image-developing devices depends on the rotating movement of the developer container in accordance with the rotation of the rotary image-developing station. It is difficult to solve the above-mentioned problem of waiting time by independently moving the developer container at an increased speed. Therefore, it is believed that there is no image forming apparatus which employs a rotary image-developing station capable of supplying developers in a highly sufficient manner without causing a waiting time when supplying the developers.